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LarryBible 12-23-2000 08:47 PM

Well I finally got around to tearing apart the engine that I pulled out of my 240D last February or so.

Background; The engine rebuild had about 120,000 miles on it. It used a quart in 1,100 or 1,200 miles since the rebuild. I was screaming along in my low geared Euro 240D manual at about 75 MPH on the freeway when I heard a terrible knocking noise in the engine. I kicked it in neutral and coasted to the breakdown lane. Once stopped, I tried to refire it. It would hit on three cylinders, then lock up. There was oil all down the back of the motor around and below number four. I called the rollback and brought it home. I put an interim engine in it which has since given up itself.

I finally got it on the engine stand this morning and rotated it by hand with no problems. I put it on top dead center and the camshaft mark lined up perfectly. There was nothing apparently wrong under the valve cover. I pulled the head and found oil in number 4 cylinder. I also found oil on the headgasket, behind number 4 cylinder. The cylinders all look very nice. Crosshatch still showing and no ridge.

It could be my imagination, but it looks like the piston is smaller in that hole. There is more gap between the piston and cylinder wall. I can see the top of the ring when pearing in there. I put a snap guage in one of the other cylinders, set it, then put in 4. The cylinder seems to be the same size. I'm wondering if that piston was maybe a standard piston. The block was bored to first O/S.

The way I was bolted to the engine stand I couldn't remove the pan. I have to get a couple of bolts to remount the bottom two engine stand arms so I can get the pan off. I am now very anxious to see what I find when I pull this piston.

I will keep everyone informed about what I find.

Merry Christmas,

LarryBible 12-24-2000 10:30 AM

I was thinking about the number four cylinder. If there was a mistakenly too small piston in the bore, there's no way it would have left the bore looking so pretty and unworn. Additionally, it would probably have made a terrible noise from the get go.

I expect to find the answer when I get the pan off.

Merry Christmas,

LarryBible 12-28-2000 06:11 PM

I got the engine rolled over and the pan off. The rod bearing on number four is gone and it took the journal with it.

There was oil on the head gasket around number four cylinder and in the cylinder also all down the back of the engine. Has anyone ever seen a head gasket fail like this? It did not lose any coolant.

Could it have lost oil pressure at the back of the engine from this and not lost coolant?

Any similar experiences would be interesting to here.

I know that these cranks are hardened. Can a crankshaft grinder turn one of these cranks and reharden it for reasonable money, or should I just find another crank?

Since the cylinders look so good, I believe I will replace the crank and bearings and leave the pistons in place.

I look forward to your responses,

mbdoc 12-28-2000 08:10 PM

The 240D crank isn't hardened like the turbo cranks. Just make sure that the crank grinder understands the metric system. .25mm isn't .010", but it is close. Pull pistons & at least look at rings & ring clearance!!!! I would at least replace rings. HAPPY NEW YEAR!! I enjoy your posts!!

Wm. Lewallen 12-28-2000 11:27 PM

240 Pistons
Larry you can check the size of the pistons by wiping the carbon off the top and see what size is stamped on it. It should be stamped Std. .25,.50,.75, or 1.00mm. Anything bigger than .25 is hard to find, but are available.
If your crankshaft is not scored too bad, maybe you can have the rod journals turned. Bearings are available in undersize up to 1.00mm. They too are hard to find, but they are available. I have used them with no problem.
Bill Lewallen Lexington,Ky.

Wm. Lewallen 12-28-2000 11:39 PM

Another thing on your crankshaft:if the rod journal is scored too bad you may be able to have that journal built up and then turned to fit whatever size bearing you use. I have done this with good results. The machine shop uses a special welding rod that is hardned.
0.25mm is not 0.10". It's 0.00984. Close but not quite 0.10"
Bill Lewallen Lexington,Ky.

LarryBible 01-02-2001 07:19 AM

Thanks very much for the responses. I did not know that the 240D crank is not hardened. I'm sure I can get it turned. I will also inspect cylinders and replace rings while I'm that deep.

Anyone have any thoughts about why this happened? Is there anything that could have restricted oil flow to the back of the engine which would blow oil past the head gasket and starve the number four rod bearing of oil?

Any thoughts are appreciated,

[Edited by LarryBible on 01-02-2001 at 07:23 AM]

Wm. Lewallen 01-02-2001 06:07 PM

240D Engine Failure
Larry, I hate to disagree with whoever said the cranksfts of the 240D engines are not hardened. All MB crankshafts are hardened(to a minimum scleroscope hardeness of 60.)
See page 03.4-318/4 Service Manual Engines 615,616,617.91.
Bill Lewallen Lexington,Ky.

Wm. Lewallen 01-02-2001 11:05 PM

240D Engine Failure
More information on crank hardness:The 240 engine has a Scleroscope of 60 according to the factory manual. On page 03.8-318/1 of the Service Manual Engine 617.94, the crankshaft journals have a hardeness of 55-74. So the turbo crank is a bit harder than the non turbo engines.
Bill Lewallen Lexington,Ky.

P.E.Haiges 01-03-2001 12:12 AM

Oil for the rod journals goes thru the groves in the main bearings and thru the holes drilled in the crankshaft to each of the rod journals. Thus a leak at the top of the engine would not affect the rod bearing for that cylinder but it might affect all the bearings if it lowered the oil pressure substantially. If the crankshaft journal is even slightly scored, the crankshaft must be reground (not "turned" as previously mentioned). I suggest regrinding all the journals to the same size and put in a new set of oversize rod bearings. Have the machine shop check the main bearing journals to see if they meet MB specs. If not, have them reground also and put in a new set of oversize main bearings.


LarryBible 01-03-2001 06:43 AM


Thanks very much for the replies. I plan on doing nothing less than regrinding all journals and replacing all bearings. I would do not do a patch up on this engine. I will also replace the rings and check everything out there. I will find someone who can do the crankshaft correctly.

My biggest concern is still finding out what caused this so that I don't put together an engine that ruins the crankshaft again. The oil in the cylinder, all over the head gasket around that cylinder, and all down the block around that cylinder is very confusing. Has anyone ever seen anything like this before.

I'm rebuilding this engine to go back in the car, just because it's an old friend and I can't stand seeing it sitting out next to the barn any more. It needs to be put back on the road even if it's nothing but a back up car for my daughter or wife.

Thanks again for your responses and have a great day,

LarryBible 01-08-2001 07:43 AM

More clues.

I pulled a little more of the engine apart yesterday and here's what I found:

All rod bearings and journals are destroyed, all main journals look pretty darn good.

This is confusing to me. I assume that the oil has to go through the mains to reach the oil holes in the rod journals. Why didn't the mains go?

I won't put money and time in this engine unless I can find the cause first.

Thanks for any comments you may offer,

P.E.Haiges 01-08-2001 10:37 AM


Usually when all the rod bearings fail there has been a lubrication failure. Did you notice if the oil pressure gage was showing any pressure when the engine failed? Check the oil pump for failure. I would suspect a bad oil pump.

I broke the end of the oil pump shaft off one time and it ruined my rod bearings and not the mains. The rod bearings take more of a beating, they are smaller than the mains and they run out of oil before the mains.

About the oil on the outside of the engine, maybe a plug in the oil line system came out or the oil pressure regulator failed. You might plug all the oil holes and apply air pressure to one hole and see if you can find any leaks. Maybe the head gasket failed where the oil goes into the head to lubricate the cam.


LarryBible 01-08-2001 01:16 PM


The head gasket failed at the back of the block. Is the camshaft feed at the back? Would this account for a total loss of pressure?

Thanks a million for the response. I guess I need to pull the oil pump and investigate. I did not think to look at the oil pressure when it occurred. All I could think was to kick in neutral and coast to the side of the road.

From what you're saying it sounds like I did indeed experience a total oil pressure loss.

Have a great day,

P.E.Haiges 01-08-2001 08:27 PM


Its been a long time since I took a camshaft off but I think the oil feed to the camshaft is thru the front cam tower. You can tell by looking for the oil passage from the block to the head. The 3/8 inch pipe that runs across the cam towers lubricates the cam lobes and the other 2 cam towers. It doesn't seem that a leak around the head gasket would take enough oil away from the bearings to destroy them. Running the rings dry may damage them too so I suggest you also replace the rings.

I had a 190Dc that really burned oil, about 50 miles per quart. Unlike a gasoline engine that fouls the plugs when it burns a lot of oil, the Diesel ran good. I thought the rings were bad but when I took it apart I found a crack in the head that was leaking lubricating oil into the combustion chamber of one cylinder. That combustion chamber was really carboned up because it was just one cylinder that was burning all the oil. Again I think it was #1.


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